This invention relates to an improved design of a pressure converter for mounting above the drill bit at the lower end of a drill pipe for deep drilling, in particular for oil and gas, for the purpose of generating an increased fluid pressure by utilizing energy in a drill fluid flow downwards through the drill pipe.
The object of the invention is to provide improvements in a pressure converter of the kind being subject to the applicant's international patent application PCT/NO90/00164, whereby it has been found possible to obtain more advantageous solutions in certain important parts of the design.
Various proposals are previously known for such utilization of the drill fluid flow, in particular in order to obtain an enhanced or more efficient drill operation. An example of such known techniques is to be found in the international patent application, PCT/EP82/00147. This example relates to the employment of an impact effect brought about with the drill fluid flow as a source of energy, so as to enhance the drilling action.
Of particular interest to the present invention is the employment of one or more high pressure jets adapted to make the drilling more effective by providing a cutting action in a surrounding rock formation. This is also previously known per se, inter alia from U.S. Pat. No. 3,112,800, which describes a method including the use of a pressure converter apparatus for generating the required high pressure. The invention, however, is directed to a novel design of a pressure converter for generating the required high fluid pressure.
International patent application PCT/NO90/00164 relates to a pressure converter comprising drive means adapted to be driven by the drilling fluid flow and to move valve means controlling piston means for reciprocating movement with a pressure stroke and a return stroke, said piston means having at one side a relatively large piston area adapted to be subjected to the drilling fluid pressure in the drill pipe during the pressure stroke, and having at the other side a first, opposite piston area which both during the pressure stroke and the return stroke is subjected to the return pressure in the drilling fluid flow upwards outside the drill pipe, and a second, opposite and relatively small piston area which during the pressure stroke is adapted to generate an increased pressure in a smaller portion of the drilling fluid flow, whereby a check valve provides for discharge of this smaller portion of the flow to a header channel which leads forward to the drill bit, whereas the large piston area during the return stroke is adapted to be subjected to the return pressure outside the drill pipe and the small piston area to the pressure in the drill pipe.